Enzymes are being increasingly used as catalysts in chemical and biochemical syntheses. Thus, in many cases, hydrolases, more especially lipases (EC 3.1.1.3), are already being used for lipolysis in industrial processes by virtue of the often relatively mild reaction conditions. These enzymes are produced by various microorganisms. To isolate the enzymes, fermentation of the microorganisms is followed by an expensive purification process. The effectiveness of these catalysts is often offset by the high costs of production and isolation, so that research groups are constantly striving to increase the yields of enzymes or the productivity of the enzymes.
The standard chemical method for producing monoglycerides involves the base-catalyzed glycerolysis of triglycerides, with a typical yield of 40 to 60% monoglyceride by weight, based on the weight of total glycerides in the final product. Further enrichment to a >90% monoglyceride content is achieved by physical separation techniques, such as molecular distillation or crystallization.
Various enzymatic routes suitable for the production of monoglycerides have been described in the literature: 1) enzymatic synthesis starting from fatty acid and glycerol; 2) enzymatic glycerolysis starting from triglyceride and glycerol which corresponds to the chemical process; 3) the 1,3-regioselective hydrolysis or alcoholysis of triglyceride. Summaries of these processes may be found, for example, in (a) Recent Rec. Devel. Oil Chem., 3(1999), 93-106; (b) Hydrolases in Organic Synthesis, Wiley-VCH (1999), eds. Bornscheuer & Kazlaukas.
Monoglycerides may only be enzymatically-synthesized effectively if water is removed from the reaction equilibrium, which removal is achieved by the addition of a molecular sieve or by a reaction in vacuo. In addition, solubilizers are required for a good synthesis (see Recent Res. Devel. Oil Chem., 3(1999)). Accordingly, the enzymatic synthesis of monoglycerides is not a cost-effective alternative to the chemical process. Enzymatic glycerolysis results in similar equilibrium adjustments to chemical glycerolysis for the production of monoglycerides. The synthesis of enriched monoglycerides (content >60%, by weight), therefore, also requires enrichment through distillation or crystallization. Accordingly, this process also is not a cost-effective alternative to the chemical process.
Published PCT Applications WO 90/13656 and WO 90/04033 (both Enzytech, Inc.) and U.S. Pat. Nos. 5,935,828 and 5,316,927 (both Zaks et al.) describe the production of monoglycerides by enzymatic alcoholysis with various alcohols and a little water in the mixture. Lipases are used in powder form or immobilized. In the Examples, the alcohol component is present in a 20-fold excess, and lipases are used in quantities of ca. 20% by weight, based on the triglyceride used.
Published PCT Applications WO 91/16441, and WO 91/16442 (both Procter and Gamble Company), and U.S. Pat. No. 5,116,745 (Mazur et al.) describe processes in which a mixed regioselective alcoholysis and hydrolysis of triglycerides to 1,2-diglycerides and 2-monoglycerides using lipases is carried out in the presence of a solvent, an alcohol and an aqueous buffer.
Published European Patent Application EP 0 407 959A2 (Lion Corporation) describes a process for the production of polyol fatty acid monoesters using an immobilized thermostable lipase in the presence of secondary or tertiary alcohols as solubilizers and reactants.
Published PCT Application WO 02/06505A1 (Nippon Suisan Kaisha Ltd.) describes regioselective alcoholysis using immobilized lipase, a large excess of alcohol and high concentration of enzyme, followed by re-esterification of the monoglyceride.
JP 03108489 and JP03187385 (Meito Sangyo Co. Ltd.) describe the regioselective hydrolysis of triglycerides with alkaline lipase in the presence of alkaline salts. The lipase used in only active under alkaline conditions.
JP 03103499 (Meito Sangyo Co. Ltd.) describes the regioselective alcoholysis of PUFA triglycerides with isobutanol in the presence of an alkaline lipase.
In the various enzymatic productions of partial glycerides that have been described in the above-cited documents, solvents are required, the water of reaction has to be removed at great expense and/or the lipases used are either very special (expensive) or immobilized. The low reaction rates compared with the conventional chemical synthesis, the long reaction times and hence high equipment utilization levels, and/or the high concentrations of alcohol to be reacted or high amounts of lipase needed, in order to achieve an acceptable yield of monoglycerides limit the utility of these processes. Even the use of inexpensive lipases leads to processes that make an industrial process impractical on cost grounds alone.
Now, the objective of the present invention was to provide an inexpensive variant to the known enzymatic production methods, in order to increase the yield of monoglycerides from polyol esters, such as triglycerides, for example, in enzymatic alcoholyses, and to keep the enzyme content to a minimum.